1. Field of the Invention
This invention relates to a cap for a gas-supply nozzle in a post-combustion bed in a hot water or steam boiler having at least two fluidizing beds, in which the flue gases from an upstream combustion bed enter a subsequent or downstream combustion bed which is provided with a number of nozzles and in which a nozzle cap is provided over each nozzle to serve as a deflecting member for guiding the flue gases into the bed material forming the post-combustion bed.
U.S. patent application Ser. No. 584,511 filed on Feb. 28, 1984, in the name of Erik Henriksson and assigned to the assignee of this application describes a method for cleaning the gas-supply nozzles in a hot water or steam boiler with two or more fluidizing beds, where at least in the bed immediately downstream of the most upstream bed (the combustion bed) surges of gas under pressure are supplied to the nozzles or the hole openings to keep the latter clear of blocking deposits. By raising the pressure of air or other gas supplied to the nozzles instantaneously, the nozzles in the post-combustion bed, through which the gases of combustion from the combustion bed flow to the upper bed, are periodically cleared of impurity deposits which, if not removed, will block the nozzles and occasion shut down of the boiler.
The above-mentioned patent application also describes a hot water or steam boiler having at least two fluidizing beds.
2. Description of the Prior Art
Problems arise in connection with the nozzles. In spite of the abovementioned supply of air, on the one hand there is a risk of clogging of a deflecting member mounted above the nozzle since the air or gas flowing through the nozzle is mixed with dust, and on the other hand there is a need to cool any such deflecting member.
It is also desirable to prevent back-flow of the bed material from the post-combustion bed back down to the lower combustion bed, to make any deflecting member used relatively insensitive to erosion, to avoid narrow passages in the bed and to obtain a good mixing of flue gas and air. Furthermore, it is desirable to improve the fluidization by reducing the pressure drop across the bed as a function of the bed height, which is important particularly in the case where the plant is operated with only a partial load on the boiler.